Filter apparatus

ABSTRACT

A tubular filter element for use in a tube-type filter includes an externally-ribbed plastic core which is hollow throughout its length and which is surrounded by a coarsely-perforated plastic sleeve. The sleeve serves to space an outer finely-perforated cake-supporting tube from the core. A pair of plastic end members fit over and are heat welded to the core and the sleeve, the upper member being apertured. The core is apertured such that liquid passing through the outer tube and the sleeve passes downwardly along the outer surface of the core and up through the hollow cavity in the core during a filtering operation and in the reverse direction during a cake removal operation.

United States Patent Schmidt, Jr. 1 Oct. 3, 1972 [54] FILTER APPARATUS3,422,958 l/ 1969 Newman ..2l/457 [72] Inventor: TIenry Schnudt, Jr.,l-lmsdale, 111. Primary Examiner keuben Friedman [73] Assignee:Industrial Filter & Pump Mfg. C0-, Assistant Examiner-Frederick F.Calvetti Cicero, lll. Attorney-Fidler, Patnaude & Lazo [22] Filed: Aug.20, 1970 [57] ABSTRACT [21] Appl' 65393 A tubular filter element for usein a tube-type filter ineludes an extemally-ribbed plastic core which ishol- [52] us. C1. .1.....210/315, 210/457, 210/497 low throughout itslength and which is u r unded by 51 Int. Cl. ..B01d 27/00 acoarsely-perforated Plastic Sleeve The sleeve serves [58] Field ofSearch ,.210/457, 458, 484, 489, 323, to Space an outer h-P eCake-Supporting 5 7 97 5 33 tube from the core. A pair of plastic endmembers fit over and are heat welded to the core and the sleeve,

d the upper member being apertured. The core is aper- [56] References Cle tured such that liquid passing through the outer tube UNITED STATESPATENTS and the sleeve passes downwardly along the outer surface of thecore and up through the hollow cavity in 2,725,144 1 H1955 Smlth et"2]0/458 the core during a filtering operation and in the reverse3,543,940 12/1970 Schm dt, Jr ..210/507 X direction during a cakeremoval operation. 3,438,502 4/1969 Schmidt, Jr. et a1...2l0/323 X3,394,815 7/1968 Harms et al. ..2l0/323 11 Claims, 8 Drawing Figures 704I4 I Y 49 I as I 42 37 PATENTEDHBT 3 I972 SHEET 2 BF 2 M/VEN TOR HENRYSCHMIDT, JR

x@/ w T LE FILTER APPARATUS The present invention relates generally tofiltration apparatus for removing entrained solids suspended in aliquid, and it more particularly relates to a new and improved filterelement for use in a tube-type filter employing apparatus for causing ahigh velocity reverse flow of liquid through the tubular filter elementsduring a cleaning operation to remove a filter cake deposited on theoutside surfaces of the elements.

Tube-type filters ordinarily employ a plurality of perforated tubularfilter elements which are interconnected between the inlet and outletportions of the unit so that as the fluid to be clarified passes fromthe inlet to the outlet it must pass through a porous filter cakedeposited on the perforate walls of the filter element. Accordingly, theentrained solids are removed from the liquid. As the solids are thusdeposited on the filter elements the porous cakes which adhere to theoutside surfaces thereof continue to increase in thickness until thefilter cakes reach some predetermined thickness where operationalefficiency is impaired. At this time, the cakes must be removed in orderto provide efficient operation of the system. Removal of the filtercakes is commonly referred to as a filter cleaning operation and isaccomplished in certain types of filters by reversing the flow of liquidthrough the filter elements thereby to dislodge the cakes. The dislodgedcake thus falls to the bottom of the filter chamber and passes outthrough a drain port.

During the normal filtering operation, in order to prevent anaccumulation of fine particles which frequently settle out of the liquidto be clarified at the inside of the filter elements and deposit on thebottom wallof the filter elements, in some applications each of thefilter elements is provided with an inner tube which is commonly knownas a blow-down tube and which extends within the cavity of the filterelement from the top of the filter element to a point near the bottomthereof. As a result, fluid passing through the filter cake and into thecavity of the filter element flows downwardly along the outer surfacesof the tube and into the bottom end thereof whereby the fluid flows at ahigh velocity into the tube near the bottom wall of the filter elementto cause any settled-out fine particles to be agitated so that they donot collect and form a heel which could be a source of contamination tothe clarified liquid and also impair the operational efficienc-y of thefilter. Moreover, during the filter cleaning cycle of operation, liquidis forced through the inner tube and then out its bottom end so that theliquid more evenly dislodges the filter cake from the filter element.

All of the foregoing requirements and features have only been met byfilter tube designs in which relatively expensive, corrosive-resistantmaterials were used since the filter elements are continually bathed inthe liquid to be clarified. Therefore, it would be desirable to providea filter element which possesses the foregoing features and which isentirely composed of plastic material so that the filter element isrelatively inexpensive to manufacture and does not become corrodedthereby to eliminate contamination problems, especially where the filteris used for processing food products. Moreover, it is desirable thatsuch a filter tube be sufficiently strong and self-supporting towithstand extremely high pressure differentials across the wallsthereof, and in many applications to withstand high operatingtemperatures. In addition, it is desirable that such tubes have asubstantially long life, and since filters require periodic maintenancewherein the tubes are removed, the filter tubes should be extremelysturdy so that when subjected to rough handling they will not bedamaged. Since a large number of filter tubes are commonly used in asingle filter, another requirement of such filter tubes is that the costthereof not be excessive.

Therefore, an object of the present invention is to provide a new andimproved tubular filter element of this general type which is entirelycomposed of plastic material and which is strong and durable inconstructron.

Another object of the present invention is to provide a new and improvedfilter element which is relatively less expensive to manufacture thanprior art type filter elements and which possesses the advantages of theheretofore known prior art filter elements.

Briefly, the above and further objects are realized in accordance withthe present invention by providing a tubular filter element whichincludes an extemallyribbed plastic core having a cavity therein and acoarsely perforated plastic sleeve surrounding and tightly fitted overthe core. The sleeve adds to the rigidity of the filter element of thepresent invention, and it serves to space an outer filter cakesupporting tube from the core. An apertured head member is sealablysecured to the core and the sleeve at one end thereof, and animperforate base member is sealably secured to the opposite end of thecore and the sleeve. The core is apertured in a manner such that liquidpassing through the tube and the sleeve passes downwardly between theribs of the core and up through the cavity of the core during afiltering operation and in the reverse direction 'during the reverseflow of liquid in a cake removal operation. Thus, the filter element ofthe present invention is entirely composed of plastic material, and isdesigned to function in the same manner as a conventional blow-down typeof filter tube without the necessity of an inner tube.

Further objects and advantages and a better understanding of the presentinvention will be had by reference to the following detailed descriptiontaken in connection with the accompanying drawings wherein:

FIG. 1 is an elevational view, partly broken away showing the manner inwhich the filter tubes embodying the present invention may be mounted inan associated filter;

FIG. 2 is a fragmentary, elevational view of a tubular filter elementembodying the present invention;

FIG. 3 is an enlarged, longitudinal sectional view of the filter elementof FIG. 2 taken substantially along the line 33 thereof; and 1 FIG. 4 isan enlarged cross-sectional view of the filter element of FIG. 2 takensubstantially along the line 4- 4 thereof.

Referring now to the drawings and more particularly to FIG. 1 thereof,there is shown a multiple tube filter 10 including as its principalelements a generally cylindrical, vertically disposed tank 12 having aconical bottom wall 14 which is connected to an inlet conduit 16 via aninlet valve 18 for supplying, under pressure, the liquids to beclarified. Supported on a tube sheet 22, a plurality of filter tubes 20depend into the filter chamber within the tank 12 and are maintained ina spaced-apart relationship by a spacer 23. A domeshaped cover 24 issealably secured in place over the tube sheet 22 and an outlet conduit26 and an outlet valve 27 are connected thereto for conveying theclarified liquid away from the filter. As will be described in greaterdetail hereinafter, the tubes 20 are substantially cylindrical in shapeand have a perforated wall surface across the interstices of whichsolids entrained in the liquid passing through the filter are trapped.In practice, a filter aid material such as a diatomaceous earth or afinely particulated asbestos is entrained in a liquid which is passedthrough the filter thereby to deposit a layer of the filter aid materialon the surfaces of the tubes 20. This layer of filter aid material isinherently porous and provides the filter media across the pores ofwhich solids entrained in the actual liquid to be clarified arecollected.

In operation, as the tank 12 is filled, the filter aid material isrecirculated via the inlet line 16 and the inlet valve 18 through thetubes 20 into the chamber in the cover 24 and thence returns through theoutlet conduit 26 to the inlet line 16. As the liquid enters the tank12, air from the portion of the tank below the tube sheet 22 is bledinto the tubes and out of the tank in a manner which is hereinafterdescribed. After a suitable precoat layer of the filter aid material hasbuilt up on the outer surfaces of the tubes 20, the filter is then readyfor operation. During the filtration operation, the entrained solids areremoved from the liquid and are deposited on the porous precoat filtercake. The operation can continue until the thickness of the cakeincreases to the point where operational efficiency is impaired. At thistime, the cakes are removed from the filter tubes 20 in a cleaningoperation.

The cleaning operation is commenced by first closing the outlet valve 27and then closing the inlet valve 18. As a result, air trapped in thedome 24 is compressed under a pressure equal to the inlet pressure tothe filter. In order to dislodge the filter cake from the filter tubes20, a large drain valve 29 at the lowermost portion of the bottom wall14 is then opened to permit the trapped air in the dome 24 to rapidlyexpand and thereby to force the liquid trapped in the dome through thefilter elements 20 and out through the drain valve 29. After dislodgingthe filter cake, the drain valve 29 is closed, and the filter isreturned to normal operation.

Considering now the filter elements in greater detail with reference toFIGS. 2, 3, 4 and 5 of the drawings, the filter element 20 comprises asits principal elements a cylindrical, externally-ribbed tubular plasticcore 31, a coarsely perforated plastic sleeve 33 surrounding and tightlyfitted over the core 31, a pair of end members 35 and 37 fitted over andsealably secured to the core 31 and the sleeve 33, and a finelyperforated filter cake supporting tube or sleeve 39 which surrounds thesleeve 33. In order to sealably secure the sleeve 33 to the filterelement 20, as best seen in FIG. 5, a centrally-apertured head collar 40surrounds a tubular connector 41, and a centrally-apertured base collar42 surrounds a mounting stud extending from the base end member 37,whereby the sleeve 33 is tightly and sealably secured to the collars bya pair of cords 44 and 44A as hereinafter described in connection withFIGS. 6-8. The core 31 is hollow throughout its length and is composedof a plastic material, such as polypropylene. A plurality oflongitudinally extending, equally-spaced ribs 45 extend throughout thelength of the core 31, and a plurality of holes 47 located near thebottom end of the core 31 open into its hollow interior. Each of theholes 47 is disposed between a pair of ribs 45 and has a diameter whichis sightly less than the distance between the ribs 45. The holes 47 arethus equally spaced about the periphery of the .core 31 and are arrangedin two separate, closely-spaced planes extending in a directionperpendicular to the axis of the filter element 20. For a filter elementwhich is 36 to 72 inches in length, it has been found that the twoplanes may be spaced apart by approximately 1 inch, and the lower planemay be spaced from the bottom end of the filter element 20 byapproximately 1 inch. Thus, due to the location of the holes 47, most ofthe fluid flowing through the fine mesh sleeve 39 and the coarselyperforated sleeve 33 during a filtering operation flows downwardly alongthe outer surfaces of the core 31 between the fluid-guiding ribs 45 andthen through the holes 47. Since the fluid is forced to enter therelatively small holes 47, the fluid flows at a high velocity near thebottom end of the core 31 to prevent an accumulation of fine particleswhich settle out of the fluid. Such an accumulation in the bottom of thetube is known as a heel and can contaminate the filtrate and interferewith the operational efficiency of the filter 10. Also, during thecleaning operation, most of the fluid flowing in a reverse directionthrough the hollow core 31 flows downwardly and out of the holes 47 atthe lower end of the core 31 to evenly dislodge the filter cake from theouter surfaces of the filter element 20. Therefore, due to the locationof the holes 47, the filter element 20 possesses the advantages of theprior known tubular filter elements having a blow-down tube.

In order to bleed the air from the portion of the tank 12 below the tubesheet 22 during filling of the tank, a single hole 49 (FIG. 2) islocated near the top end of the core 31 between a pair of ribs 45. Thus,the tank 12 need not be provided with a vent below the tube sheet 22,thereby reducing cost of the filter apparatus of the present invention.

The coarsely perforated sleeve 33 serves to space the outer fine meshsleeve 39 from the core 31, and it also serves to add to the rigidity ofthe filter element 20. The sleeve 33 is a grid of tubular constructionand is formed of an extruded thermoplastic material, such aspolypropylene. The grid consists of a plurality of rods or filaments 50which are integrally united at the points of intersection with aplurality of transverse filaments or rods 52. One material of this typeis sold by E. I. du Pont de Nemours & Co. under the trademark Vexar andis formed in a continuous extruding process whereby the filaments 50 and52 are continuous and are integrally united at the cross-over points toform a seamless tube. Thus, the filaments 50 and 52 are interconnectedin the form of a mesh or grid to provide a coarsely-perforated sleeve.

Referring now to FIG. 4, the top end member 35 is a generally cup-shapedhead member which is composed of a plastic material, such aspolypropylene. The head member 35 fits over the upper end of the core 31and has a centrally-disposed depending plug member 54 which tightly andsealably fits into the upper end of the hollow cavity in the core 31 sothat the externallyribbed wall 55 of the core 31 and the sleeve 33 fitssnugly between the plug member 54 and an annular outer wall 56 of thehead member 35. A centrallydisposed threaded aperture 58 in the headmember 35 communicates with the cavity in the core 31 and is adapted toreceive the externally-threaded connector 41 (FIG. 5) for connection tothe tube sheet 22, whereby the cavity in the filter element can beconnected in fluid communication with the chamber within the dome 24.

The lower end member 37 is a generally cup-shaped base member which isidentical to the head member 35 except that there is no holetherethrough. Accordingly, the cap member 37 is also composed of aplastic material, such as polypropylene. In order to seal over the lowerend of the hollow core 31, a centrallydisposed imperforate plug member61 on the base member 37 fits tightly and sealably into the lower end ofthe cavity of the core 31 and receives the externallyribbed wall 55 andthe sleeve 33 between the plug member 61 and an outer wall 63 of thebase member 37. A centrally-disposed threaded recess 65 in the outerface of the base member 37 is adapted to receive the externally-threadedmounting stud 43 (FIG. 5) for mounting the filter element 20 on thespacer 23 in the tank 12.

In order to sealably and rigidly connect the head member 35 and the basemember 37 to both the core 31 and the sleeve 33, the head member and thebase member are heat welded to the core 31 and thesleeve 33 by anysuitable technique, such as spin welding, whereby the entire tubularfilter element 20 is thus formed into a rigid integral unit in an easyand inexpensive manner. For the purpose of facilitating the weldingprocess, pairs of diametrically opposed recesses 67 and 69 are providedin the outer faces of the head member and the base member 37,respectively, so that the assembled unit can be readily held in amandrel for spin welding purposes.

Referring now to FIGS. 5, 6, 7 and 8 of the drawings, the collars 40 and42 are composed of an elastomeric material, such as rubber, and arecentrally-apertured to permit them to be slipped over the ends of theconnector 41 and the stud 43, respectively, and to be posi tionedagainst the respective outer faces of the head member and base member37. In order to sealably secure the sleeve 39 to the filter element 20,a centrally-disposed external circumferential groove 70 in the rubbercollar 40 and a similar groove 72 in the base collar 42 receives therespective cords 44A and 44 and the adjacent portion of the sleeve 39 toseal the sleeve 39 to the collars 40 and 42. For the purpose of sealingthe collars 40 and 42 to the connector 41 and-the stud 43, respectively,the collars 40 and 42 snugly surround the connector 41 and the stud 43,respectively.

In order to dress the filter element 20 with the filtercake supportingsleeve 39, the sleeve 39 is slipped over the filter element 20 until theend of the sleeve is approximately aligned with the bottom edge of thebase collar 42. The cord 44 is then wrapped about the outer surface ofthe bottom portion of the sleeve 39 opposite the peripheral groove 72 inthe collar 42. The cord 44 is then pulled tightly about the sleeve 39and tied in place to seat the cord 44 and the adjacent portion of thesleeve 39 in the groove 72 of the base collar 42 and to compress thecollar 42 about the stud 43. A free end loop 74 of the cord 44 as shownin FIG. 6 is then slipped over the end of the mounting stud 43 so thatwhen the filter element 20 is mounted on an upstanding pin 76 of thegrid-like space 23 in the filter tank 12, the end loop 74 also surroundsthe pin 76 and thus is restrained. As shown in FIGS. 7 and 8, the upperend of the sleeve 39 is similarly tied with the cord 44A about thesleeve 39 opposite the peripheral groove in the upper collar 40. Theexcess material 78 at the upper end of the sleeve 39 can then be foldedover the cord 44A to restrain a free end 81 of the cord 44A.

In order to readily tie the cords in place, and also to permit the cordsto be readily untied for removal of the sleeve 39, each of the cords,such, for example, as the cord 44A, comprises a loop of cord, such aspolypropylene braided cord or other suitable cord, which is tied in aloop with a square knot or other suitable knot. The loop is then wrappedabout the outer surface of the sleeve 39 opposite the peripheral groove72 in the collar 42, and the end 81 of the loop is slipped through theopposite end 83 of the loop of cord 44A and then pulled back and slippedunder one of the cords of the loop. The loop 81 is then pulled tight tocause the cord 44A and the adjacent portion of the sleeve 39 to bewedged into the groove 72 of the collar 42, thereby firmly seating thecord 44A in place.

In view of the foregoing description of the disclosed embodiment of thepresent invention, it should now be apparent that the filter element ofthe present invention includes an externally-ribbed plastic core whichis hollow throughout its length, and a coarsely-perforated plasticsleeve which spacesan outer finely-perforated tubular cake supportingmedium from the inner core. A pair of plastic end members are heatwelded to the core and the sleeve to provide a sturdy unitaryconstruction, which is relatively inexpensive and easy to manufactureand which is able to withstand high pressure differentials. Since thefilter unit of the present invention is composed entirely of plasticmaterial, the unit will not corrode even after repeated use in highlycorrosive materials. Moreover, the filter element of the presentinvention possesses all of the advantages of prior art tubular filterelements having blow-down tubes without the necessity of an inner tube.In this regard, due to the location of the holes in the core, the filterelement of the present invention prevents the accumulation of fineparticles at the bottom of the inside of the element, and it permits thefilter cake to be evenly dislodged during the cleaning operation.

While the present invention has been described in connection with aparticular embodiment thereof, it will be understood that those skilledin the art may make many changes and modifications without departingfrom the true spirit and scope of the invention. Therefore, by theappended claims it is intended to cover all such changes andmodifications as come within the true spirit and scope of thisinvention.

What is claimed is:

1. A filter element for use in a filter having means for providing areverse flow of fluid through the filter element, said filter elementincluding a unitary, tubular, plastic core having a plurality ofcontinuous external ribs extending longitudinally throughout the lengthof said core,

a head member sealably bonded over the upper end of said core and havinga passageway therethrough opening into said core,

an imperforate base member sealably bonded over the bottom end of saidcore,

a coarsely perforated plastic sleeve surrounding and tightly fittingover said core from said head member to said base member, said sleevebeing bonded to said head and base members, and

a fine mesh sleeve removably positioned over said plastic sleeve, I

said core being essentially imperforate except near the bottom where itis provided with a plurality of radial passageways extendingtherethrough,

whereby liquid passing into the filter element through said sleevesflows downwardly between said ribs along the outside of said core to thebottom thereof, through said passageways into said core and upwardlythrough the central cavity in said core.

2. A filter element according to claim 1, wherein said core includesmeans defining a given number of passageways near said one end forpassing air during filling thereof, and means defining a relativelylarger number of apertures near said other end for passing the bulk offluid during the filter operation and during the cake removal operation.

3. A filter element according to claim 2, wherein said given number isl, and said larger number of passageways are equally-spaced about theperiphery of said core and are arranged in two separate, closelyspacedplanes extending in a direction perpendicular to the axis of said filterelement, said planes being disposed within a given distance from theouter end of said base member, said given distance being less than 10percent of the length of said filter element.

4. A filter element according to claim 2, wherein said core is composedof polypropylene.

5. A filter element according to claim 2, wherein said coarselyperforated plastic sleeve comprises a grid of tubular construction, saidgrid consisting of a plurality of first filaments and a plurality oftransverse filaments integrally connected at the points of intersectionwith said first filament to form a seamless tube.

6. A filter element according to claim 5, wherein said sleeve iscomposed of polypropylene.

7. A filter element according to claim 5, wherein said head member has adepending, annular outer wall and includes a centrally-disposeddepending plug member tightly fitting into the cavity at said one end ofsaid core so that said core and said sleeve fit snugly between said plugmember and the outer wall of said head member.

8. A filter element according to claim 5, wherein said head member iscomposed of polypropylene.

9. A filter element according to claim 7, wherein said base member hasan upstanding annular wall and includes a centrally-disposed plug memberfitting tightly into said other end of said core, said core and saidsleeve being positioned between said plug member and the outer wall ofsaid base member and being bonded thereto such that the filter elementis a rigid integral l o. A filter element according to claim 8, whereinsaid base member is composed of polypropylene.

11. A filter element for use in a filter having means for reversing theflow of liquid through the filter element to remove a filter cakedeposited thereon, said filter element including a tubular core overwhich a finely perforated filter cake supporting medium is mounted, theimprovement comprising a unitary tubular, plastic core having aplurality of longitudinally extending external ribs,

a head member sealably secured by bonding over one end of said core andhaving an axial passageway therethrough opening into said core,

an imperforate base member sealably secured by bonding over the otherend of said core, and

a coarsely perforated, seamless plastic sleeve surrounding and tightlyfitting over said core,

said core being provided with a plurality of radial passagewaysextending therethrough,

a tubular connector connecting to said head member and communicatingwith said axial aperture in said head member,

a mounting stud connected to said base member,

an elastomeric centrally-apertured head collar surrounding saidconnector,

an elastomeric centrally-apertured base collar sealably surrounding saidmounting stud,

said collars each having an external, annular peripheral groove, and

a pair of cords each arranged in a continuous loop and securing a filtercake supporting medium to said collars, said cords being seated in saidgrooves of said collars whereby when secured in place, said cords sealsaid filter cake supporting medium to said collars.

1. A filter element for use in a filter having means for providing areverse flow of fluid through the filter element, said filter elementincluding a unitary, tubular, plastic core having a plurality ofcontinuous external ribs extending longitudinally throughout the lengthof said core, a head member sealably bonded over the upper end of saidcore and having a passageway therethrough opening into said core, animperforate base member sealably bonded over the bottom end of saidcore, a coarsely perforated plastic sleeve surrounding and tightlyfitting over said core from said head member to said base member, saidsleeve being bonded to said head and base members, and a fine meshsleeve removably positioned over said plastic sleeve, said core beingessentially imperforate except near the bottom where it is provided witha plurality of radial passageways extending therethrough, whereby liquidpassing into the filter element through said sleeves flows downwardlybetween said ribs along the outside of said core to the bottom thereof,through said passageways into said core and upwardly through the centralcavity in said core.
 2. A filter element according to claim 1, whereinsaid core includes means defining a given number of passageways nearsaid one end for passing air during filling thereof, and means defininga relatively larger number of apertures near said other end for passingthe bulk of fluid during the filter operation and during the cakeremoval operation.
 3. A filter element according to claim 2, whereinsaid given number is 1, and said larger number of passageways areequally-spaced about the periphery of said core and are arranged in twoseparate, closely-spaced planes extending in a direction perpendicularto the axis of said filter element, said planes being disposed within agiven distance from the outer end of said base member, said givendistance being less than 10 percent of the length of said filterelement.
 4. A filter element according to claim 2, wherein said core iscomposed of polypropylene.
 5. A filter element according to claim 2,wherein said coarsely perforated plastic sleeve comprises a grid oftubular construction, said grid consisting of a plurality of firstfilaments And a plurality of transverse filaments integrally connectedat the points of intersection with said first filament to form aseamless tube.
 6. A filter element according to claim 5, wherein saidsleeve is composed of polypropylene.
 7. A filter element according toclaim 5, wherein said head member has a depending, annular outer walland includes a centrally-disposed depending plug member tightly fittinginto the cavity at said one end of said core so that said core and saidsleeve fit snugly between said plug member and the outer wall of saidhead member.
 8. A filter element according to claim 5, wherein said headmember is composed of polypropylene.
 9. A filter element according toclaim 7, wherein said base member has an upstanding annular wall andincludes a centrally-disposed plug member fitting tightly into saidother end of said core, said core and said sleeve being positionedbetween said plug member and the outer wall of said base member andbeing bonded thereto such that the filter element is a rigid integralunit.
 10. A filter element according to claim 8, wherein said basemember is composed of polypropylene.
 11. A filter element for use in afilter having means for reversing the flow of liquid through the filterelement to remove a filter cake deposited thereon, said filter elementincluding a tubular core over which a finely perforated filter cakesupporting medium is mounted, the improvement comprising a unitarytubular, plastic core having a plurality of longitudinally extendingexternal ribs, a head member sealably secured by bonding over one end ofsaid core and having an axial passageway therethrough opening into saidcore, an imperforate base member sealably secured by bonding over theother end of said core, and a coarsely perforated, seamless plasticsleeve surrounding and tightly fitting over said core, said core beingprovided with a plurality of radial passageways extending therethrough,a tubular connector connecting to said head member and communicatingwith said axial aperture in said head member, a mounting stud connectedto said base member, an elastomeric centrally-apertured head collarsurrounding said connector, an elastomeric centrally-apertured basecollar sealably surrounding said mounting stud, said collars each havingan external, annular peripheral groove, and a pair of cords eacharranged in a continuous loop and securing a filter cake supportingmedium to said collars, said cords being seated in said grooves of saidcollars whereby when secured in place, said cords seal said filter cakesupporting medium to said collars.